Apple maggots

How to identify apple maggot

The adult fly is 1/4 inch long, smaller than a common housefly.

• It has dark markings on the clear wings and a conspicuous white spot where the thorax joins the abdomen.
• Has three (male) or four (female) white stripes on the abdomen.

Life cycle of apple maggot

Adult apple maggots begin to emerge from the soil around July 1, continuing through most of the summer.

• Adult flies often leave and feed outside the orchard, in wooded or brushy areas.
• They return to lay eggs just under the skin of apples.
• Each female fly can lay hundreds of eggs.
• Once eggs hatch, larvae feed for three to four weeks.
• When apples drop to the ground, the larvae transform into pupae in the soil.
• Pupae spend the winter underground, emerging as adults the following summer.

Damage caused by apple maggot

• Apple maggot flies lay eggs in fruit which becomes pitted and misshapen.
• The female fly creates a "sting” or hole as she lays an egg; each one forms a tiny spot or dimple.
• Maggots (larvae) tunneling through the flesh break down the pulp, and it discolors and starts to rot.
• Larvae are rarely seen.

How to protect your trees from apple maggots

Keep your garden clean

• Frequently pick up and remove any apples that fall during the growing season and after harvest.
• Put these apples in the trash or send them to a municipal composting site.
• Do not compost them in your yard.

Removing overripe and rotten apples from around your trees can help reduce apple maggot infestations, but it will not prevent apple maggot flies that come in from other areas.

Bag apples

This method was developed in western Minnesota and should be used after you thin the fruit in early to mid-June.

• Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples.
• Snip the bottom corners off each bag with a pair of scissors to leave a small opening for water to run out.
• At harvest, remove the bag.

Bagging fruit takes extra time, however, the apples are protected from apple maggots for the rest of the season.

Bagging is easy to do if you have a small to medium-sized tree that can be managed from the ground or a short ladder.

If you have a tall tree, you may choose to bag only the fruits that are easy to reach, and let the apple maggots have the fruit growing higher up.

Sticky traps

Apple maggot traps are red spheres coated with tanglefoot, a sticky substance that permanently holds insects. They capture apple maggot females that attempt to lay eggs on the fruit.

Types of apple traps

• Wooden or plastic spheres painted red.
• Red plastic spheres sold specifically for this purpose.
• Store-bought large, red, fresh apples coated with tanglefoot. Compost them at the end of the season.
• The Ladd trap is a red sphere and yellow rectangle combination. This trap may be more effective in catching apple maggot flies, even though they can be harder to clean. 

Whichever type of trap you choose, the spheres or apples should be at least 3 inches in diameter and bright red.

• Hang up wooden spheres with an eye screw and a wire hook.
• Hang up fresh apples by skewering the apple with a coat hanger and bending the excess wire into a hook.
• Hang scent lures that smell like apples with your traps to make them more attractive to flies. 
• Hang one trap per 100 fruit (after thinning) in each tree.
  • One or two spheres for small trees and five or more traps for larger trees.
  • Place at least one trap on the side of the tree that faces any wooded or brushy area.
  • A second trap should hang on the south side of the tree.

To further reduce apple maggot pressure, hang traps in apple or hawthorn trees in wooded or landscaped areas nearby.

• Hang traps in the trees by the end of June, to catch the apple maggot flies as they first attempt to lay eggs.
• Remove any leaves or fruit touching the traps.
• Check all the traps weekly. Clean off the tanglefoot-coated insects and apply more tanglefoot as needed.

Kaolin clay

Kaolin clay can discourage apple maggot flies and other insects from laying eggs in apple trees. This method is best used with traps and before any pesticide application. 

• Apply clay in a visible layer to all surfaces of the tree, leaves and fruit. This acts as a visual and physical repellent to insects.
• Apple maggot females are attracted to the red color of ripening apples, so a grayish-white apple is not attractive.
• The layer of clay on fruits repels many insects and they may leave immediately.
• Clay washes off easily even in moderate rain and may not provide enough coverage.
• As fruits expand or clay washes off, reapply.
• A well-maintained coating of kaolin clay can protect 90 percent of fruit from apple maggots but requires more effort than other methods.

Pesticides

Check for the presence of apple maggots using sticky red spheres. This will help you decide if you should apply a pesticide. 

• Check the trap frequently.
• If you do not use a scent lure, spray for apple maggots as soon as you catch a single adult.
• If you hang a trap with a lure, wait until you have caught a total of five flies.

Effective pesticides available for apple maggot control are esfenvalerate, carbaryl and spinosad.

• Traps need to be cleaned after each spray.
• Reapply tanglefoot if needed and begin checking the traps every day or two as before.
• Spray again and repeat the whole process, as needed.
• You might have to spray for apple maggot three or four times per season.

Fortunately, the number of apple maggot adults reduces as the season progresses and you should be able to stop spraying sometime in August.